Phonograph

Phonograph is a device that reproduces sounds that have been recorded on audio records. Phonographs are also called record players. Until the mid-1980's, they were the most common device for listening to music and other sound recordings. Today, most people have replaced their record collections with cassette tapes and compact discs. Compact disc players produce better sound than phonographs do. Compact discs also are more durable than records. However, many people still use phonographs to listen to older recordings.

How phonographs work. Phonographs play records that have been produced by a process called analog disc recording. In this process, an analog (likeness) of the original sound waves is stored as jagged waves in a spiral groove on the surface of a plastic disc. As the disc rotates on the phonograph, a needle, called a stylus, rides along the groove. The waves in the groove cause the stylus to vibrate. These vibrations then are transformed into electric signals and converted back into sound by speakers.

Most phonograph records are thin plastic discs with a diameter of 7 or 12 inches (18 or 30 centimeters). A 7-inch record is played at a speed of 45 revolutions per minute (rpm) and has only a few minutes of sound per side. A 12-inch long-playing (LP) record is played at 331/3 rpm and holds about 30 minutes of sound per side. A 12-inch single holds several minutes of sound per side and is also generally played at 331/3.

Parts of a phonograph. There are six main parts of a phonograph. These parts are: (1) the turntable, (2) the drive system, (3) the stylus, (4) the cartridge, (5) the tone arm, and (6) the amplifier.

The turntable is a flat metal plate covered with rubber on which the record sits. Most turntables operate at 331/3 and 45 rpm. Some turntables also operate at 78 rpm, a playback speed used in making records until the 1950's.

The drive system spins the turntable. Most phonographs are equipped with a direct drive.

In a direct drive system, the turntable is mounted directly on the motor shaft. The speed of the motor, which can be varied, determines the speed of the turntable's rotation.

The stylus is a piece of diamond or extremely hard synthetic material shaped somewhat like a cone. It is suspended from one end of a flexible strip of metal. The other end of the metal strip is attached to the cartridge.

The stylus vibrates as it rides in the groove of a record. In a stereophonic phonograph, the stylus responds to two separate sets of waves--one on either side of the groove. These two sets of waves correspond to the two stereo sound channels.

The cartridge< receives vibrations from the stylus and transforms them into electric energy. Most cartridges generate voltages when the motion of the stylus moves an electric coil in a magnetic field or moves a magnet near a coil. A stereophonic cartridge changes the stylus vibrations into two sets of electric signals--one for the right sound channel and one for the left.

The tone arm, also called the pickup arm, holds the cartridge and stylus. In most record players, the tone arm is mounted on a pivot. The pivot lets the stylus ride the record groove in an arc across the disc. The pressure of the stylus is controlled by a weight at the pivot end of the tone arm. Too much pressure causes poor sound quality and increased record wear. If there is too little pressure, the stylus will skip across the record. Wires along the tone arm carry electric signals from the cartridge to the amplifier.

The amplifier boosts the power of the weak signals from the cartridge so that they reach the speakers in sufficient strength. The speakers convert the electric signals to sound waves (see Speaker).

How phonograph records are made. The production of most records begins with making a master (original) tape recording in a studio or concert hall. Such recordings are made using tape recorders capable of recording many separate tracks (channels of sound). In producing the master tape, an engineer records different instruments or groups of instruments on separate tracks. During recording, various aspects of sound quality can be controlled separately for each track. In addition, each track can be recorded and played back alone or in combination with other tracks. See Recording Industry.

Often, the engineer records several takes (separate recordings) of a section of music. After recording, the editing engineer selects the best take of each section of music. The engineer edits the music electronically to create a new master tape. The new tape has the sections from different takes arranged as though they had been recorded in a single performance. The engineer uses a process called mixdown to reduce the number of tracks to the two needed for a stereophonic record.

The next step in making a phonograph record is the creation of a master lacquer. A lacquer is an aluminum disc coated with nitrocellulose lacquer. A blank lacquer is rotated on the turntable of a machine called a record-cutting lathe. Electric signals from the master tape are fed to a cutting head on the lathe. A cutting stylus on the cutting head cuts a wavy, V-shaped groove that spirals toward the center of the disc. This stylus is connected to two electric coils. Each electric coil is near a separate electromagnet.

In making a stereo lacquer, electric signals corresponding to the right channel magnetize one coil. Those corresponding to the left channel magnetize the other coil. The magnetic changes in the coils cause the stylus to move up and down and from side to side. The stylus thus cuts waves for the left channel on one side of the groove, and it cuts waves for the right channel on the other.

Next, a metal master is made from the master lacquer by a process called electroplating. In this process, the surface of the master lacquer is coated with nickel. When separated from the lacquer, this nickel plate froms a metal master--a negative copy that has ridges where the lacquer has grooves. Plating the metal master produces a mother--a positive copy of the lacquer. The mother itself is then plated several times to create multiple negative copies called stampers.

Two stampers, one for each side of the disc, are mounted in a hydraulic press. A piece of plastic called a biscuit is placed between the stampers and squeezed in the press. Steam circulating through the press softens the plastic, which is imprinted with record grooves from both stampers. After the record is imprinted, cool water stiffens the disc.

History. The first practical phonograph was invented in 1877 by the U.S. inventor Thomas A. Edison. Edison's device could record sound on tinfoil wrapped around a small metal cylinder, and then replay the sound. The cylinder rotated on an axle that was turned with a hand crank. A needle attached to a diaphragm (vibrating disc) was placed against the cylinder. As someone spoke into a mouthpiece, the sound waves made the diaphragm and needle vibrate. These vibrations caused the needle to make dents in the foil on the rotating cylinder. To play back the sound, another needle attached to a diaphragm was placed against the cylinder. As the cylinder was rotated, the dents in the foil made the needle and diaphragm vibrate. These vibrations created sounds roughly like the original sound. This type of recording is called acoustic recording because the sound is produced without electrical energy.

In 1885, the U.S. scientists Chichester Bell and Charles S. Tainter improved upon Edison's invention by recording on cardboard cylinders coated with wax. This new recording material produced better sound.

In 1887, Emile Berliner, a German immigrant to the United States, invented the Gramophone--a phonograph that used shellac discs. These discs provided better sound, were more durable, and could be mass-produced more easily than could cylinders.

The first electrically recorded phonograph records appeared in 1925. In addition, manufacturers began producing phonographs with electric motors and amplifiers, which greatly improved the quality of recorded sound.

Until 1948, most commercial disc recordings were made of a mixture of clay and shellac and were played at 78 rpm. In that year, the plastic 33 1/3-rpm LP record appeared on the market. It had been developed at the Columbia Broadcasting System Laboratories under the direction of Peter Goldmark, a U.S. electrical engineer. The LP held much more recorded sound and was more durable than the 78-rpm disc. In 1949, the 45-rpm disc was introduced by Radio Corporation of America (now RCA Corporation) to compete with the LP.

Growing interest in high fidelity in recorded sound led to the appearance of stereophonic phonographs and discs in 1958. Previously, records and phonographs were monaural, or monophonic. Such records and record players reproduce sounds from only one channel. By the late 1960's, almost all new phonographs and records were stereophonic.

Audio compact discs were introduced in Japan and Europe in 1982, and in the United States in 1983. Their superior sound quality and durability quickly made them popular. Today, few new recordings are issued on phonograph records.

Contributor: Ken C. Pohlmann, M.S.E.E., Prof. of Music Engineering, Univ. of Miami.

Additional Resources

Millard, Andre. America on Record: A History of Recorded Sound. Cambridge, 1995.

Nakajima, Heitaro, and Ogawa, Hiroshi. Compact Disc Technology. IOS Pr., 1992.

Rumsey, Francis, and McCormick, Tim. Sound and Recording: An Introduction. 2nd ed. Focal Pr., 1994.

Welch, Walter L., and Burt, L. B. S. From Tinfoil to Stereo: The Acoustic Years of the Recording Industry, 1877-1929. Univ. Pr. of Fla., 1994.

Phonograph

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